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Genetic and Rare Diseases Information Center (GARD)

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What is polymyositis?

What is the typical long term prognosis for people with polymyositis?

What is polymyositis?

Polymyositis is one of a group of muscle diseases known as the inflammatory myopathies, which are characterized by chronic muscle inflammation accompanied by muscle weakness.  Polymyositis affects skeletal muscles (those involved with making movement) on both sides of the body.  It is rarely seen in persons under age 18; most cases are seen in adults between the ages of 31 and 60.[1] The cause of polymyositis is not fully understood.[2][3] Although there's no cure for polymyositis, treatment can improve muscle strength and function.[1][2]
Last updated: 4/22/2009

What is the typical long term prognosis for people with polymyositis?

The long term prognosis for people with polymyositis is highly variable. Some people experience only mild weakness and respond well to treatment. Others experience a rapid progression of symptoms and do not respond to any therapy. Rarely, people with polymyositis recover spontaneously without any treatment. People with polymyositis tend to have a better outcome if they receive treatment right away, have mild muscle weakness, have no difficulty swallowing, and have no signs of disease in other organ systems such as the heart and lungs.[4]
Last updated: 10/31/2011

  1. NINDS Polymyositis Information Page. National Institute of Neurological Disorders and Stroke (NINDS). 2009; Accessed 11/18/2010.
  2. Mayo Clinic Staff. Polymyositis. July 10, 2009; Accessed 11/18/2010.
  3. Pappu R, Seetharaman M. Polymyositis. eMedicine. November 6, 2009; Accessed 11/18/2010.
  4. Darras BT. Patient information: Myositis. In: Basow, DS. UpToDate. Waltham, MA: UpToDate; 2011;